Core collection . It is a primary and well-organized source of genes. With a structure given by partitions or strata formed by sets of accessions that present some degree of genetic similarity. Having this structure in the core collection and in the reserve collection allows associating levels of diversity to each stratum. Unquestionably, strata with greater diversity should have a higher proportion of accessions.
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- 1 Size
- 2 Structure
- 3 practical reasons for establishing a core collection
- 4 What materials represent the core collection?
- 5 Validation of a core collection
- 6 Collections of clonal cultures
- 7 Sources
The large size of some collections could discourage their use and it was proposed to establish, from an existing collection, a limited or core collection, conceptually defined as one that, with a minimum of representativeness, groups the genetic diversity of a plant species. Due to their size, they include between 10 and 20% of the original collection but have 70-80% of their total diversity. Accessions that are not included in the core collection will not be removed, but will instead form the reserve collection. Even a random selection from a germplasm collection can be used as the core collection. This sampling process may be the simplest, but perhaps the least effective, since it would not represent genetic diversity because they do not use information on accessions. The use of such information always improves the representativeness of a core collection. However, whether the procedure adopted is simple or complex, it is always advisable to consult genebank administrators, plant breeders and other researchers interested in the cultivated species and the use that will be made of its genetic diversity.
The structure of the nucleus does not replace the collection or the material from which it is obtained and has been proposed as an inexpensive alternative to promote the evaluation of germplasm, as well as being an effective tool to improve its conservation and use. The fact of representing the diversity present in the entire collection, together with the identification and elimination of duplicate accessions, currently constitute two of the complementary solutions aimed at improving the management, conservation and efficient and sustainable use of germplasm.
Practical reasons for establishing a core collection
- The fact that it represents a rational way of prioritizing materials for their characterization and evaluation
- Improve management strategies and distinguish priorities for the search for new materials
In this way, with reduced costs and efforts, the data bank would include much more information and a faster and more efficient use of germplasm.
The Global Plan of Action for the Conservation and Sustainable Use of Plant Genetic Resources for Food and Agriculture recommends among its main activities, in addition to increasing characterization and evaluation, the increase in the number of core collections, since the correct use Smaller in structure, it is important in the efficient and effective management of collections, and in turn, increases and facilitates the use of conserved phylogenetic resources worldwide.
What materials represent the core collection?
The material or collection that will be represented by the core collection will be different in each case, depending on the material available, which constitutes a prudent set of material for the establishment of the core collection and the objectives for which said core is established. .
In addition, it is pointed out that there is no fixed and appropriate proportional size or ratio for all core collection cases. It is recommended to include in the core collection 10% of accessions of the total collection, provided that this number does not exceed 2000. They concluded that the fraction of an optimal sample depends, to a large extent, on the degree of genetic redundancy between the accessions, of the resources available to maintain the entries of the core collection and their regeneration frequency. Although an optimal value could not be specified, a proportional ratio of 20% to 30% is considered adequate. Other sizes, from 5% to 10% are optimal because they capture between 75% and 90% of the diversity. On the other hand, higher percentages (20% to 30%) have also been suggested,
A core collection can effectively represent the genetic diversity of the entire collection, if the accessions are first separated into groups with some significance (stratification), maximizing the variation between them and minimizing the variation within them. In order to define the groups, in general, a gradual and hierarchical procedure is followed. Several approaches have been applied to decide the number of entries that each group should have, one consists of assigning entries to the group according to the number of accessions that appear within it, another alternative is to compare the diversity of markers within the groups when There is information on characterization and justify the allocation of inputs. There is finally a subjective approach that takes into account for allocation,
To establish a core collection, it is necessary to choose the entries that will make it up. These should be the ones that best represent the group and those that best fulfill the function and objectives of the core collection in terms of the group’s genetic diversity, the quality of the documentation, the availability of seeds or propagation material, among others. The choice can be made more or less randomly or based on a formal analytical procedure or practical considerations.
Validation of a core collection
Once the core collection is established, it is necessary to check whether the original objectives of representing diversity and avoiding repetition have been achieved. This validation process generally includes comparing the kernel, by some appropriate method, with the original collection from which it was developed. This comparison can be made between the averages, ranges, frequencies and variances of some of the characters present in the different groups of the core collection, with those belonging to the groups from which the basic ones were derived. The ranges should remain similar, while the averages should approach the median; The variances may increase in the core collection.
While in seed-producing crops a small number of samples is surprisingly efficient in retaining alleles at a simple loci , in clonal or vegetatively propagated crops such as malanga or guagüí, which rarely or never produces seeds in natural conditions. in Cuba , the interest around the entire genotype increases much more, since specific combinations of genes in highly heterozygous constitutions can be a valuable conservation. In this case, the number of genotypes preserved increases in direct proportion to the number of samples (assuming duplicates are removed), and there is no special efficiency in sampling in small numbers.
Clonal culture collections
In order of magnitude, they are smaller than the collections of seed crops and by nature have fewer accessions, therefore the need to create a nucleus in these crops is discussed, and if necessary, if it should be greater or less than in seed collections. However, a combination of several factors indicates that a base collection of a clonal culture has much to gain from the establishment of a core collection.
Factors that encourage the need to create core collections in vegetatively propagated crops:
- The costs and vulnerability of field collections that increase with their size.
- The development and validation of new in vitroconservation methods .
- Monitoring the health of preserved samples.
- The effective evaluation of an increased range of characters and their interactions to provide genotypes for direct use.
- The provision of genotypes for introduction into new areas or for new purposes.
- The high cost of producing and maintaining a pathogen-free clonal material for distribution.
However, group formation and selection of entrances to the nucleus should give greater emphasis to the phenotypic characteristics expressed in the relevant environment than in the case of seed crops. Core development needs more data integration in these crops than in seed collections, and the proportion of inputs should not be set at 10%, as a greater or lesser proportion may be required to fulfill the special roles of the collections. clonal nucleus, previously analyzed.